The ability to make separable electrical contact with contacts of miniature electronic circuits has become more problematic as the mechanical, electrical, and reliability requirements of these electrical contacts become more demanding. Nano springs, pogo pins, micro springs, and other miniature contact devices have been developed to deal with the problem of making reliable electrical contact between a microcircuit and the rest of an electronic system. The problem for the industry, however, is that no particular contact design appears to provide all of the properties required, even where specially designed contact elements are used in specific applications. None of the existing contacts can meet all of the design criteria.
It is desirable to have separable electrical connections in electronic applications because these connections are used in system assembly, device testing, and wafer probing.
As frequencies, densities, and the number of connections increase for a packaged electrical device, existing electrical connector technologies do not function effectively. This occurs as frequencies increase above ˜1 GHz, densities increase to a contact-to-contact spacing (pitch) of 1 mm or less, and the number of connections increases to 600 or more. The malfunctioning of the connecting system effectively means that large clamping forces, on the order of 50 g/contact or higher, are often required. Also, these poorly performing contact systems show poor signal integrity (noise more than 3 dB or >˜0.5 nH self inductance), or DC poor contact resistance (>15 mOhms).
Other common problems associated with the existing contact technologies are: (i) the inability to scale to high density, (ii) the inability to address large pin counts, (iii) the inability to address low profile requirements or unique form factors, (iv) high cost, (v) inadequate reliability, (vi) poor mechanical compliance to surface under contact while maintaining good electrical performance, (vii) high insertion force required to make good electrical contact, (viii) high inductance, and (ix) poor signal integrity at high frequencies.
Existing technologies can address some of the problems for some market requirements, but they cannot address all of the aforementioned problems, even for specific applications.
The trend in electronics has been to increase backend circuit density and performance in order to realize a correlation to Moore's Law, which states that semiconductor density or performance doubles nearly every 18 months. This push to emulate Moore's Law drives the design of electrical contact elements that are optimized mechanically, thermally, and electrically for use in high-speed electronic systems. The contact elements may be used to attach a microprocessor for a computer, a telecommunications NPU network device, or a host of other electronic devices that are possible in the electronics industry.
Optimizing mechanical and electrical properties of the contact elements is also required to enable highly reliable and reproducible semiconductor testing results. This is essential for preventing potential early device or product failure. To be competitive, companies have had to optimize their devices on a cost/performance basis. However, this type of optimizing leads to inefficiencies and additional costs for thoroughly testing the devices. Neglecting a thorough testing of the devices, however, may lead to early field failure at the customer site. This dichotomy is very problematical for the manufacturer.
In some cases, such as for silicon-wafer probing and mobile applications, it is also very important that: (a) the interconnections be scalable to high densities, (b) that the contacts use the least possible amount of real estate on the printed circuit board, and (c) that they provide minimal impact on the printed circuit board wiring.
In some cases, such as for laptop computers, handheld devices, and high-frequency applications, it is very important that the height of the connectors and the auxiliary circuit members be as low as possible.
As aforementioned, new requirements relating to system performance have increased dramatically as circuits have continued to shrink in size and improve performance. This has impacted the stringent specifications for interconnections in these systems. For example, signal integrity requirements have become extremely demanding. Signal integrity can be improved by designing the interconnections to match the electrical impedance of the system, thus minimizing electrical reflections.
The need for improved electrical performance using separable and reconnectable electrical contact elements have led to a wide variety of connector solutions in the marketplace. These solutions cause pressure upon the industry to assure effective repair, upgrade, and/or replacement of various components of the system (e.g., connectors, cards, chips, boards, modules, etc.).
It is desirable to have a connector element, designed to provide a demountable connection that would provide good performance (<0.5 nH self inductance, <3 dB noise, <50 g contact force, <15 mOhms contact resistance) for frequencies above ˜1 GHz and a pitch ˜1 mm or less for an array of ˜600 contacts or greater.
The present invention comprises an electrical contact structure in which the elastic working range approaches or exceeds the electrical contact distance and the pitch and height are both equal to or less than 1 mm. This contact structure provides the desired performance under the constraints of high-end applications as described above.
The reason that the working range needs to be on the order of the contact length is that surfaces of the structures being connected are never perfectly flat. As the required height and pitch of the connections decreases to 1 mm or less and the number of electrical contacts in a connector array increases to about 600 contacts or more, the inherent non-flatness of the structures that are being connected prevents good electrical connection from being made unless the working range is on the order of the electrical contact distance.
It would therefore be desirable to have a contact system that can meet the many requirements for miniature contacts for both special and across-the-board applications, and have an elastic and electrical functionality across the gap between the electrical members to be connected.
It is also highly desirable in some cases that, within the final product, such connections be separable and reconnectable in the field. Such a capability is also desirable during manufacture to facilitate testing and manufacturing rework, for example.
The present invention features a new contact system that meets all, or most of, the aforementioned requirements. The elasticity and flexibility of the contacts of the present system exceed anything currently in the marketplace. The range of flexibility is such that the contacts can be deflected across the full gap between the electrical devices being connected and beyond, i.e., the contacts are movable across the full substrate (interposer) thickness. To the best of knowledge and belief, no other contact system has this capability.
The current invention is based on the discovery that a reliable contact system first needs to be designed with a contact elasticity within a given range without sacrificing electrical properties, and as a corollary to this requirement, the contacts must be engineered within a given size range for the elasticity chosen.
The present invention provides a scalable, low cost, reliable, compliant, low profile, low insertion force, high density, separable/reconnectable electrical connection for high speed, high performance semiconductors and electronic circuitry. The invention can be used, for example, to make electrical connections from a Printed Circuit Board (PCB) to another PCB, MPU, NPU, or other semiconductor device. The invention comprises, but is not limited to, a beam land grid array (BLGA) or a ball beam grid array (BBGA) system. The electrical and mechanical functionality of the BLGA and/or BBGA system lends itself to numerous applications in electronic space. This is particularly so where scalable, low cost, reliable, compliant, low profile, low insertion force electrical contacts are required.
Together, these two systems provide a good signal integrity electronic test contact element for high speed, high performance applications. Short interconnections are made possible between almost any electrical contact surfaces of the system, while maintaining high electrical performance. Some suitable applications include test, burn-in, prototyping, and full wafer burn-in applications that require high electrical performance. Optimized electrical, thermal, and mechanical properties have been realized.
Both the BBGA and the BLGA systems offer inductive and elasticity advantages over stamped metal springs and coiled springs. Low inductance is important for signal integrity at high frequencies. In general, shorter contact elements give lower inductance but less elastic working range. This is not the case with the BLGA and BBGA systems. The lowest inductance pogo pins in the market are 0.4 nH and they are very expensive. All the current approaches are reaching fundamental limitations in reducing the inductance because they become too hard to manufacture (e.g., pogo pins), or too stiff (e.g., stamped metal springs). These and other like systems cannot operate with the correct geometry to allow for low inductance. By contrast, the contact array system of the present invention can flex across the entire gap separating the electrical devices to be connected.
The number of I/O(s) on high-end packages is several thousand and increasing. This strains the requirement for low contact force. At present, high performance production sockets with 1,000 or more I/O require the application of several hundred pounds of force, in order to make an effective connection with an LGA socket. As the I/O count increases, these systems cannot be assembled in the field due to the required high force.
In addition, the power in many systems continues to increase. This in turn strains the thermal requirement. More heat must be removed from the silicon die, which causes the manufacturers to directly clamp a heat sink onto the top of the silicon die. In some cases, this is done with no cap on the package for protection. A small contact force is necessary for electrical connection to prevent damaging the device, using a thin cap or cap-free design that enhances thermal conduction.
The invention provides a very low contact force solution. In test sockets, a lower contact force enables a less expensive handling system. Both the BBGA and the BLGA systems offer many advantages over other conventional connector technologies, one of which is a contact wiping force having both horizontal and vertical force components.
Typical LGA contact elements need to operate over a range of compression distances. The extended range accommodates variations in system co-planarity, and can accommodate a less flat system. This significantly reduces cost for the overall design because it allows for a less expensive clamping solution and relaxed specifications on the two interfaces being connected. A larger elastic working range is also correlated to better connector reliability.
The spacing between contact elements has to be scaled down with respect to the package I/O pitch. Current technologies, such as stamped springs and injection-molded approaches, are fundamentally limited in how closely they can be spaced during manufacture. Stamped springs need room to be inserted, and injection-molded parts need space for the mechanical integrity of the mold. The present contact array system has no such limitations. By contrast, the inventive contact system is functional across the entire gap of separation between the devices to be connected, i.e., it spans the thickness of the substrate.